1. Field of the Invention
The present invention relates to a sheet processing apparatus that performs predetermined processing on a sheet recording medium that has been conveyed therein, such as a paper sheet, a recording sheet, a transfer sheet, and an overhead projector (OHP) sheet (simply referred to as a “sheet” herein and in the claims), and an image forming system including the sheet processing apparatus and an image forming apparatus such as a copying machine, a printer, a facsimile, and a digital multifunction peripheral (MFP).
2. Description of the Related Art
Conventional image forming systems have been widely used that include a sheet processing apparatus that performs predetermined processing such as middle folding processing and saddle stitch bookbinding processing. The middle folding processing folds a single sheet of an image formed sheet. The saddle stitch bookbinding (or binding) processing aligns a bundle of a plurality of sheets, staples the bundle of sheets, and thereafter folds them. In addition, the following sheet processing technology has already been known: the sheets or the bundle of sheets on which the middle folding processing or the saddle stitch binding processing has been performed are conveyed through the apparatus so that the folded portions of the sheets or the bundle of sheets are at the leading end in the sheet conveying direction, and then stacked on a stacking tray in a state in which the sheets or the bundles of sheets partially overlap with each other.
The conventional technologies as described above are publicly known and disclosed in Japanese Patent No. 4179011 and Japanese Patent Application Laid-open No. 2010-143677, for example. A sheet processing apparatus as described below is disclosed in Japanese Patent No. 4179011. The sheet processing apparatus aims to stack bundles of sheets that have been bundled and folded in two parts in order, regardless of the size of the sheets, on a book tray. The sheet processing apparatus includes a sheet receiving unit, a sheet bundling unit, a sheet folding unit, a sheet stacking unit. The sheet stacking unit stacks the bundles of sheets, each of which has been folded by the sheet folding unit that folds the bundles of sheets, each of which has been bundled by the sheet bundling unit that bundles the sheets, each of which has been placed on the sheet receiving unit that receives a sheet from an image forming apparatus. A conveying roller member is provided above the sheet stacking unit of the sheet processing apparatus. The conveying roller member conveys the bundle of sheets folded by the sheet folding unit downward the sheet stacking unit. The sheet processing apparatus also includes a sheet size recognition unit that recognizes the size of a sheet placed on the sheet receiving unit. The sheet stacking unit includes a sheet conveying member. While the sheet stacking unit consecutively places each of the bundles of sheets conveyed from above by the conveying roller member, the sheet conveying member moves each of the bundles of sheets placed on the sheet stacking unit step by step. According to the recognition result of the size of the sheet, the conveying distance in a step of the sheet conveying member for sequential conveyance of the bundles of sheets can be changed.
A sheet stacking unit with the following structure is disclosed in Japanese Patent Application Laid-open No. 2010-143677. The sheet stacking unit stacks the bundles of sheets including a plurality of sheets on which folding processing has been performed in a state in which the bundles of sheets partially overlap with each other. This aims to solve the problem that the bundle of the sheets on which folding processing has been performed tends to swell and the folded portion of the bundle of the sheets tend to open in an ejecting tray at a slant, and to appropriately stack the bundles of the sheets under such poor conditions. The sheet stacking unit includes a sheet placement portion, a sheet conveying unit, a sheet position detection means, a sheet holding means, and a control unit. The sheet placement portion is provided so that the downstream side in the sheet conveying direction of the sheet placement portion in the sheet conveying direction is higher than the opposite side and stacks the bundle of sheets on which folding processing has been performed. The sheet conveying unit conveys the bundles of sheets stacked on the sheet placement portion and overlapping with each other. The sheet position detection means detects that the trailing end of the bundle of sheets has reached a predetermined standby position on the sheet placement portion. The sheet holding means is provided swingably or slidably on the upstream side of the sheet placement portion and includes a sheet contact portion that contacts the top surface of the bundles of sheets stacked on the sheet placement portion. The control unit controls the sheet conveying unit. When a conveyed bundle of sheets overlaps onto another bundle of sheets on which folding processing has been performed and stacked on the sheet placement portion, the control unit controls the sheet conveying unit to convey the bundle of sheets, on which folding processing has been performed, stacked on the sheet placement portion, in the sheet conveying direction. If the sheet position detection means detects that the trailing end of the bundle of sheets, on which folding processing has been performed, has reached the predetermined standby position on the sheet placement portion, the control unit controls the sheet conveying unit to stop.
Japanese Patent No. 4179011 and Japanese Patent Application Laid-open No. 2010-143677 disclose the following sheet processing technologies for conveying and stacking sheets. Specifically, the bundles of sheets on which middle folding processing or saddle stitch binding processing has been performed, are conveyed so that the folded portions of the bundles of sheets are at the leading end in the sheet conveying direction. A part of a stacking tray is stored below to enable users to output a large amount of bundles of sheets and eject them without limitation.
Japanese Patent No. 4179011 discloses the following structure. The bundles of sheets are sequentially conveyed by the sheet conveying member in a state in which the bundles of sheets partially overlap with each other so that the bundles of sheets are stacked on a saddle stitch binding stacking tray in order, regardless of the size of the sheets. According to the recognition result of the size of the sheet, the conveying distance for sequential conveyance of the bundles of sheets can be changed. In the invention disclosed in Japanese Patent No. 4179011, however, it is not taken into account that the bundles of sheets are dropped from above the sheet stacking unit to store the bundles of sheets in a storage box.
When a user performs limitless ejecting, in which the bundles of sheets are dropped down from the sheet stacking unit into the storage box, as described in Japanese Patent No. 4179011, the bundles of sheets may open after being dropped down. When the subsequent bundles of sheets are dropped down in this state, the preceding bundles of sheets may be damaged.
Japanese Patent Application Laid-open No. 2010-143677 discloses the structure for appropriately stacking bundles of sheets on a sheet placement portion that is tilted so that the downstream side in the sheet conveying direction is higher than the opposite side. In the invention disclosed in Japanese Patent Application Laid-open No. 2010-143677, however, it is not taken into account that the bundles of sheets are dropped from above the sheet placement portion to store the bundles of sheets in a storage box. When a user performs limitless ejecting, in which the bundles of sheets are dropped down from the sheet placement portion into the storage box, the bundles of sheets may open after being dropped down in the same manner as described in Japanese Patent No. 4179011. When the subsequent bundles of sheets are dropped down in this state, the preceding bundles of sheets may be damaged.
In the examples disclosed in Japanese Patent No. 4179011 and Japanese Patent Application Laid-open No. 2010-143677, the bundles of sheets dropped down from the sheet stacking unit into the storage box are not aligned with each other because they are stacked or stored therein in the state as they are when dropped down. The bundles of sheets are stored in such a state that they are not aligned with each other, therefore, a user has to take the bundles of sheets out of the storage box and manually align them with each other.
The embodiment according to the present invention aims to prevent a user from manually aligning the bundles of sheets dropped down from the sheet stacking unit and stacked, and prevent the dropped bundles of sheets from being damaged.